U.S. patent application number 13/948401 was filed with the patent office on 2014-01-23 for method and system for a high capacity cable network.
This patent application is currently assigned to MaxLinear, Inc.. The applicant listed for this patent is MaxLinear, Inc.. Invention is credited to Timothy Gallagher, Curtis Ling, Sridhar Ramesh.
Application Number | 20140022926 13/948401 |
Document ID | / |
Family ID | 49946471 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140022926 |
Kind Code |
A1 |
Ling; Curtis ; et
al. |
January 23, 2014 |
METHOD AND SYSTEM FOR A HIGH CAPACITY CABLE NETWORK
Abstract
A cable modem termination system (CMTS) may communicate with a
plurality of cable modems using a plurality of orthogonal frequency
division multiplexed (OFDM) subcarriers. The CMTS may determine a
performance metric of each of the cable modems. For each of the
OFDM subcarriers and each of the cable modems, the CMTS may select
physical layer parameters to be used for communication with that
cable modem on that OFDM subcarrier based on a performance metric
of that cable modem. The parameters may be selected for each
individual modem and/or each individual subcarrier, or may be
selected for groups of modems and/or groups of subcarriers. The
parameters may include, for example, one or more of: transmit
power, receive sensitivity, timeslot duration, modulation type,
modulation order, forward error correction (FEC) type, and FEC code
rate.
Inventors: |
Ling; Curtis; (Carlsbad,
CA) ; Ramesh; Sridhar; (Carlsbad, CA) ;
Gallagher; Timothy; (Encinitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MaxLinear, Inc. |
Carlsbad |
CA |
US |
|
|
Assignee: |
MaxLinear, Inc.
Carlsbad
CA
|
Family ID: |
49946471 |
Appl. No.: |
13/948401 |
Filed: |
July 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61674733 |
Jul 23, 2012 |
|
|
|
Current U.S.
Class: |
370/252 |
Current CPC
Class: |
H04L 12/2898 20130101;
H04L 5/006 20130101; H04L 5/001 20130101; H04L 12/2801 20130101;
H04L 5/0046 20130101; H04L 41/083 20130101; H04L 1/0003 20130101;
H04L 27/2646 20130101; H04L 1/0009 20130101; H04W 24/10
20130101 |
Class at
Publication: |
370/252 |
International
Class: |
H04L 12/24 20060101
H04L012/24 |
Claims
1. A method comprising: in a cable modem termination system (CMTS)
which communicates with a plurality of cable modems using a
plurality of orthogonal frequency division multiplexed (OFDM)
subcarriers: determining a performance metric of each of said cable
modems; and for each one of said plurality of OFDM subcarriers and
each one of said cable modems, selecting physical layer parameters
to be used for communication with said one of said cable modems on
said one of said OFDM subcarriers based on said performance metric
of said one of said cable modems.
2. The method of claim 1, wherein said performance metric is a
signal-to-noise ratio (SNR) profile across said OFDM
subcarriers.
3. The method of claim 2, wherein: said plurality of cable modems
belong to a single service group; and said physical layer
parameters are selected such that a threshold SNR required for
receiving a packet broadcast to said service group is higher than a
subset of said SNR profiles corresponding to a subset of said cable
modems.
4. The method of claim 3, wherein contents of said packet are
partially or fully retransmitted to said subset of modems in a
unicast or multicast packet.
5. The method of claim 4, wherein a portion of a message recovered
from said packet broadcast to said service group is combined, in
said subset of said cable modems, with a portion of said message
recovered from said unicast or multicast packet to reconstruct said
message.
6. The method of claim 1, wherein said selecting said physical
layer parameters includes selecting whether to use hierarchical
modulation for communication with said one of said cable
modems.
7. The method of claim 6, comprising selecting to use hierarchical
modulation for a particular one of said OFDM subcarriers when a
difference between a performance metric measured for a first one of
said cable modems on said particular one of said OFDM subcarriers
and said performance metric measured for a second one of said cable
modems on said particular one of said OFDM subcarriers is greater
than a predetermined amount.
8. The method of claim 6, comprising communicating with said cable
modems using hierarchical modulation, wherein: both of more
significant bits and less significant bits are transmitted on a
first subset of said OFDM subcarriers for which each of said modems
has a relatively-high value of a performance metric; and only more
significant bits are transmitted on a second subset of said OFDM
subcarriers for which one or more of said modems has a
relatively-low value of said performance metric.
9. The method of claim 1, comprising selecting said physical layer
parameters such that there is excess capacity on a first subset of
said OFDM subcarriers and a capacity deficit on a second set of
said OFDM subcarriers.
10. The method of claim 1, comprising transmitting, on said first
subset of said OFDM subcarriers, parity bits for packets sent on
said second subset of said OFDM subcarriers.
11. The method of claim 1, comprising transmitting, on said first
subset of said OFDM subcarriers, replacement bits for packets sent
on said second subset of said OFDM subcarriers.
12. The method of claim 1, wherein said physical layer parameters
include one or more of: transmit power, receive sensitivity,
timeslot duration, modulation type, modulation order, forward error
correction (FEC) type, and FEC code rate.
13. A system comprising: a cable modem termination system (CMTS)
operable to: communicate with a plurality of cable modems using a
plurality of orthogonal frequency division multiplexed (OFDM)
subcarriers; determine a performance metric of each of said cable
modems; and for each one of said plurality of OFDM subcarriers and
each one of said cable modems, select physical layer parameters to
be used for communication with said one of said cable modems on
said one of said OFDM subcarriers based on a performance metric of
said one of said cable modems.
14. The system of claim 13, wherein said performance metric is a
signal-to-noise ratio (SNR) profile across said OFDM
subcarriers.
15. The system of claim 14, wherein: said plurality of cable modems
belong to a single service group; and said physical layer
parameters are selected such that a threshold SNR required for
receiving a packet broadcast to said service group is higher than a
subset of said SNR profiles corresponding to a subset of said cable
modems.
16. The system of claim 15, wherein contents of said packet are
fully or partially retransmitted to said subset of modems in a
unicast or multicast packet.
17. The system of claim 13, wherein said selecting said physical
layer parameters includes selecting whether to use hierarchical
modulation for communication with said one of said cable
modems.
18. The system of claim 17, wherein said CMTS is operable to select
use of hierarchical modulation for a particular one of said OFDM
subcarriers when a difference between a performance metric measured
for a first one of said cable modems on said particular one of said
OFDM subcarriers and a said performance metric measured for a
second one of said cable modems on said particular one of said OFDM
subcarriers is greater than a predetermined amount.
19. The system of claim 17, wherein said CMTS is operable to
communicate with said cable modems using hierarchical modulation,
wherein: both of more significant bits and less significant bits
are transmitted on a first subset of said OFDM subcarriers for
which each of said modems has a relatively-high value of a
performance metric; and only more significant bits are transmitted
on a second subset of said OFDM subcarriers for which one or more
of said modems has a relatively-low of a performance metric.
20. The system of claim 13, wherein said CMTS is operable to select
said physical layer parameters such that there is excess capacity
on a first subset of said OFDM subcarriers and a capacity deficit
on a second set of said OFDM subcarriers.
21. The system of claim 13, wherein said CMTS is operable to
transmit, on said first subset of said OFDM subcarriers, parity
bits for packets sent on said second subset of said OFDM
subcarriers.
22. The system of claim 13, wherein said CMTS is operable to
transmit, on said first subset of said OFDM subcarriers,
replacement bits for packets sent on said second subset of said
OFDM subcarriers.
23. The system of claim 13, wherein said physical layer parameters
include one or more of: transmit power, receive sensitivity,
timeslot duration, modulation type, modulation order, forward error
correction (FEC) type, and FEC code rate.
Description
PRIORITY CLAIM
[0001] This patent application makes reference to, claims priority
to and claims benefit from U.S. Provisional Patent Application Ser.
No. 61/674,733 titled "Method and System for a High Capacity
Television Network" and filed on Jul. 23, 2012.
[0002] The entirety of the above-mentioned application is hereby
incorporated herein by reference.
INCORPORATION BY REFERENCE
[0003] This application also makes reference to:
[0004] U.S. patent application Ser. No. 13/553,328 titled "Method
and System for Client-Side Message Handling in a Low-Power Wide
Area Network," and filed on Jul. 19, 2012;
[0005] U.S. patent application Ser. No. 13/485,034 titled "Method
and System for Server-Side Message Handling in a Low-Power Wide
Area Network," and filed on May 31, 2012;
[0006] U.S. patent application Ser. No. 13/553,175 titled "Method
and System for a Low-Power Client in a Wide Area Network," and
filed on Jul. 19, 2012;
[0007] U.S. patent application Ser. No. 13/553,195 titled "Method
and System for Server-Side Handling of a Low-Power Client in a Wide
Area Network," and filed on Jul. 19, 2012;
[0008] U.S. patent application Ser. No. ______ (attorney docket no
25051US02) titled "Method and System for Noise Suppression in a
Cable Network," and filed on the same date as this application;
and
[0009] U.S. patent application Ser. No. ______ (attorney docket no
25052US02) titled "Method and System for Service Group Management
in a Cable Network," and filed on the same date as this
application.
[0010] The entirety of each of the above-mentioned applications is
hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0011] Certain embodiments of the invention relate to cable/DOCSIS
networks. More specifically, certain embodiments of the invention
relate to a method and system for a high-capacity cable/DOCSIS
network.
BACKGROUND OF THE INVENTION
[0012] Conventional cable/DOCSIS networks can be inefficient and
have insufficient capacity. Further limitations and disadvantages
of conventional and traditional approaches will become apparent to
one of skill in the art, through comparison of such systems with
some aspects of the present invention as set forth in the remainder
of the present application with reference to the drawings.
BRIEF SUMMARY OF THE INVENTION
[0013] System and methods are provided for a high-capacity
cable/DOCSIS network, substantially as shown in and/or described in
connection with at least one of the figures, as set forth more
completely in the claims.
[0014] These and other advantages, aspects and novel features of
the present invention, as well as details of an illustrated
embodiment thereof, will be more fully understood from the
following description and drawings.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0015] FIG. 1 is a diagram of an example cable/DOCSIS network.
[0016] FIG. 2A depicts an example method of determining locations
of CMs within the HFC network.
[0017] FIGS. 2B-2D depict SNR versus frequency plots for an example
cable/DOCSIS network.
[0018] FIG. 2E depicts per-channel/subcarrier selection of
communication parameters based on measured performance metrics of a
plurality of cable modems.
[0019] FIG. 3 illustrates example transmissions in an OFDM
cable/DOCSIS network in which different values of one or more
physical layer communication parameters can be used for different
transmissions.
[0020] FIG. 4 illustrates an example implementation in which
error-correcting bits are sent on higher-SNR subcarriers to
compensate for reception errors on lower-SNR subcarriers.
DETAILED DESCRIPTION OF THE INVENTION
[0021] As utilized herein the terms "circuits" and "circuitry"
refer to physical electronic components (i.e. hardware) and any
software and/or firmware ("code") which may configure the hardware,
be executed by the hardware, and or otherwise be associated with
the hardware. As used herein, for example, a particular processor
and memory may comprise a first "circuit" when executing a first
one or more lines of code and may comprise a second "circuit" when
executing a second one or more lines of code. As utilized herein,
"and/or" means any one or more of the items in the list joined by
"and/or". As an example, "x and/or y" means any element of the
three-element set {(x), (y), (x, y)}. As another example, "x, y,
and/or z" means any element of the seven-element set {(x), (y),
(z), (x, y), (x, z), (y, z), (x, y, z)}. As utilized herein, the
term "exemplary" means serving as a non-limiting example, instance,
or illustration. As utilized herein, the terms "e.g.," and "for
example" set off lists of one or more non-limiting examples,
instances, or illustrations. As utilized herein, circuitry is
"operable" to perform a function whenever the circuitry comprises
the necessary hardware and code (if any is necessary) to perform
the function, regardless of whether performance of the function is
disabled, or not enabled, by some user-configurable setting.
[0022] FIG. 1 is a diagram of an example cable/DOCSIS network. The
example network comprises a cable modem termination system (CMTS)
102, a fiber node 104, amplifiers 106.sub.1-106.sub.3, a
directional coupler 108, splitters 110.sub.1-110.sub.3, and cable
modems (CMs) 112.sub.1-112.sub.5.
[0023] The CMTS 102 may comprise circuitry operable to manage
connections to the CMs 112.sub.1-112.sub.5. This may include, for
example: participating in ranging operations to determine physical
layer parameters used for communications between the CMTS 102 and
CMs 112.sub.1-112.sub.5; forwarding of dynamic host configuration
protocol (DHCP) messages between a DHCP server and the CMs
112.sub.1-112.sub.5; forwarding of time of day messages between a
time of day server and the CMs 112.sub.1-112.sub.5; directing
traffic between the CMs 112.sub.1-112.sub.5 other network devices
(e.g., Ethernet interfaces of the CMTS 102 may face the Internet,
Optical RF interfaces of the CMTS 102 may face the CMs, and the
CMTS may direct traffic between and among the Ethernet and Optical
RF interfaces); and managing registration of the CMs
112.sub.1-112.sub.5 to grant the cable modems network (e.g.,
Internet) access. The registration process for a CM 112.sub.X (X
between 1 and 5 for the example network of FIG. 1) may comprise the
CM 112.sub.X sending a registration request along with its
configuration settings, and the CMTS 102 accepting or rejecting the
cable modem based on the configuration settings. The registration
process may additionally comprise an exchange of security keys,
certificates, or other authentication information.
[0024] The fiber node 104 may comprise circuitry operable to
convert between optical signals conveyed via the fiber optic cable
103 and electrical signals conveyed via coaxial cable 105.
[0025] Each of the amplifiers 106.sub.1-106.sub.3 may comprise a
bidirectional amplifier which may amplify downstream signals and
upstream signals, where downstream signals are input via upstream
interface 107a and output via downstream interface 107b, and
upstream signals are input via downstream interface 107b and output
via upstream interface 107a. The amplifier 106.sub.1, which
amplifies signals along the main coaxial "trunk" may be referred to
as a "trunk amplifier." The amplifiers 106.sub.2 and 106.sub.3
which amplify signals along "branches" split off from the trunk may
be referred to as "branch" or "distribution" amplifiers.
[0026] The directional coupler 108 may comprise circuitry operable
to direct downstream traffic incident on interface 109a onto
interfaces 109b and 109c, and to direct upstream traffic incident
on interfaces 109b and 109c onto interface 109a. The directional
coupler 108 may be a passive device.
[0027] Each of the splitters 110.sub.1-110.sub.3 may comprise
circuitry operable to output signals incident on each of its
interfaces onto each of its other interfaces. Each of the splitters
110.sub.1-110.sub.3 may be a passive device.
[0028] Each of the cable modems (CMs) 112.sub.1-112.sub.5 may
comprise circuitry operable to communicate with, and be managed by,
the CMTS 1102 in accordance with one or more standards (e.g.,
DOCSIS). Each of the CMs 112.sub.1-112.sub.5 may reside at the
premises of a cable/DOCSIS subscriber.
[0029] The components (including, fiber optic cables, coaxial
cables, amplifiers, directional couplers, splitters, and/or other
devices between the CMTS 102 and the CMs 112.sub.1-112.sub.5 may be
referred to as a hybrid fiber coaxial (HFC) network. Any of the
amplifiers, directional coupler, and splitters may be referred to
generically as a coupling device.
[0030] FIG. 2A depicts an example method of determining locations
of CMs within the HFC network. Determining the locations may
include determining one or more measured performance metrics for
any particular CM 112X or group of CMs. A measured performance
metric may be, for example, an SNR-related metric such as noise
levels, strength of received desired signals, SNR at a particular
frequency, SNR over a range of frequencies (an SNR profile), bit
error rate, symbol error rate, and/or the like. Although various
implementations using SNR-profile as the pertinent performance
metric are described herein, other implementations may use a
different metric. As shown in FIG. 2A, to determine one or more
measured performance metric(s) for any particular CM 112.sub.X or
group of CMs, the CMTS 102 may transmit, at time 1, a message 202
that is destined (unicast, multicast, or broadcast) for the CM(s)
and that functions as a probe to enable determination of the
metric(s) for the CMs. The message 202 may be sent on multiple
channels spanning multiple frequencies. Similarly, where OFDM is
used for communications between the CMTS 102 and the CM(s), the
message 202 may be transmitted on each subcarrier, or may be sent
on a subset of subcarriers and then interpolation may be used for
determining the metric(s) of subcarriers on which the message 202
was not sent.
[0031] The message 202 may be transmitted with such encoding,
modulation, and transmit power such that even a CM 112.sub.X with a
worst-case performance metric(s) can receive the message and
accurately measure the metric(s). In this regard, FIG. 2B shows a
SNR versus frequency graph for an example HFC network that uses
eight channels/subcarriers. The line 222 in FIG. 2B represents a
composite worst-case SNR profile for one or more CM(s) in the HFC
network to which the message 202 is destined. For example, line 222
may be a SNR profile for a single CM 112.sub.X to which the message
202 is to be unicast. As another example, the line 222 may be a
composite worst-case SNR profile for a plurality of CMs 112 of a
particular service group to which the message 202 is to be
multicast. As another example, the line 222 may be a composite
worst-case SNR profile for all CMs of an HFC network handled by the
CMTS 102 to which the message 202 is to be broadcast. The message
202 may be transmitted such that the minimum SNR needed to receive
and accurately measure the SNR profile is below the line 222 (e.g.,
SNR needed for receiving the message 202 may be the line 224).
[0032] Upon receipt of the message 202, a CM 112.sub.X may measure,
over the channels/subbands on which the message was sent, one or
more metrics (e.g., SNR versus frequency profile) for the
transmission 202. The CM 112.sub.X may then report the metric(s)
back to the CMTS 102 via a message 204. In an example
implementation, the message 202 may contain information about when
and/or how the CM(s) are supposed to report their metric(s) (e.g.,
SNR profiles) back to the CMTS 102. In this regard, the message 202
may contain information that is the same as and/or or analogous to
what may be found in a MAP, UCD, and/or other MAC management
message defined in a DOCSIS standard. Accordingly, the message 202
may have specified a format of the message 204 and that the message
204 is to be transmitted at time T+.DELTA..
[0033] Once the metric(s) of one or more CM(s) are known to the
CMTS 102, physical layer communication parameters to be used for
communications between the CMTS 102 and the CM(s) may be determined
based on the metric(s). Physical layer parameters may be
configured/coordinated using upstream and/or downstream MAP
messages, upstream channel descriptors (UCDs), other MAC management
messages defined in DOCSIS protocols, and/or purpose-specific
messages tailored to configuring the parameters based on one or
more measured performance metric(s) as described in this
disclosure. Physical layer communication parameters may be
determined per CM based on each CM's respective metric(s) (e.g.,
each CM's SNR profile), per-service group based on a composite
metric(s) of the CM(s) assigned to that service group (e.g.,
composite SNR profile for the CM(s) of that service group), per
physical region of the HFC network based on a composite metric of
the CMs located in that physical region (e.g., composite SNR
profile for the CM(s) in that physical region), and/or the like.
Furthermore, once the metric(s) of a CM 112.sub.X is determined,
the CMTS 102 may assign that CM 112.sub.X to one or more service
groups based on its metric(s). Example physical layer parameters
include: encoding parameters, modulation parameters, transmit
power, receive sensitivity, timeslot duration, channel(s) or
subcarrier(s) on which to listen, channel(s) or subcarrier(s) on
which to transmit, and/or the like. Example encoding parameters
include: type of forward error correction (FEC) to be used (e.g.,
Reed-Solomon, LDPC, etc.), FEC block size, FEC code rate, etc.
Example modulation parameters include: type of modulation (e.g.,
frequency shift keying (FSK), phase shift keying (PSK), quadrature
amplitude modulation (QAM), etc.), modulation depth, modulation
order, etc.
[0034] In an example implementation, the transmission of messages
202, the calculation of the metrics, such as an SNR profile, by the
CM(s), the transmission 204, and subsequent configuration of
physical layer parameters based on the metric(s) may take place in
parallel with other operations performed during the
registration/ranging process.
[0035] Referring now to FIG. 2C, there is again shown the line 222
which represents an applicable SNR profile (e.g., an individual SNR
profile if configuring physical layer parameters per CM, a
composite SNR profile for a service group if configuring physical
layer parameters per service group, or a composite SNR profile for
a particular physical region if configuring physical layer
parameters based on physical location within the HFC network). Also
shown is a line 226 corresponding to SNR utilization for
communications with the CM(s) associated with the profile 222.
Assuming the distance 228 is the minimum desired headroom (e.g., to
allow for noise, etc.), then the physical layer communication
parameters resulting in line 226 are nearly optimal in the sense
that there is minimal headroom on each of channels/subbands 1, 3,
4, 6, 7, 8, and only slightly more than minimal headroom on
channels/subbands 2 and 5.
[0036] FIG. 2D illustrates example SNR profiles for the network of
FIG. 1. The light solid line 236 represents the SNR profile of CM
112.sub.1, the dashed line 222 represents the SNR profiles of CMs
112.sub.2 and 112.sub.3 (which are assumed to be the same for
simplicity of illustration), the heavy solid line represents the
reported SNR profiles of CMs 112.sub.4 and 112.sub.5 (which are
assumed to be the same for simplicity of illustration). The SNR
profiles of 112.sub.4 and 112.sub.5 may be lower than the others
because, for example, higher device and/or cable losses (e.g., as a
result of poor-performing coupling devices and/or longer cables).
In an example implementation, given the profiles 232, 234, and 236,
the CMTS 102 may reserve lower-frequency channels/subcarriers for
communications with CMs 112.sub.4 and 112.sub.5 and may reserve
higher-frequency channels/subcarriers for communications with from
CMs 112.sub.1, 112.sub.2, and 112.sub.3. In this regard, in this
example implementation, SNR falls off as the distance to the CMTS
102 increases and falls off faster at higher frequencies than at
lower frequencies, resulting in .DELTA.2>.DELTA.4 and
.DELTA.1>.DELTA.3. Thus, whereas the SNR of CMs 112.sub.4 and
112.sub.5 in channel/subcarrier 1 is only .DELTA.4 less than the
SNR of CM 112.sub.1 in channel/subcarrier 1, the SNR of CMs
112.sub.4 and 112.sub.5 in channel/subcarrier 8 is .DELTA.2 less
than the SNR of CM 112.sub.1 in channel/subcarrier 8. Thus, by
using channel/subcarrier 8 for CM 112.sub.1 and channel/subc1 for
CMs 112.sub.4 and 112.sub.5, there is a net SNR increase of
.DELTA.2-.DELTA.4 (i.e., communications to CM 112.sub.1 lose
.DELTA.4 in SNR but communications to CMs 112.sub.4 and 112.sub.5
gain .DELTA.2 in SNR).
[0037] FIG. 2E illustrates per-channel/subcarrier selection of
communication parameters based on measured SNR (as an example of a
measured performance metric) in an OFDM CATV network. Each of the
graph 242.sub.M (M between 1 and 8) is a histogram showing, for a
hypothetical HFC network comprising 20 cable modems and using 8
channels/subcarriers, the number of CMs modems that reported each
SNR value on subcarrier M. For simplicity of illustration, the SNR
levels in FIG. 2E are normalized and range from 1 to 16 (the number
16 was chosen arbitrarily and is non-limiting). In the example
implementation, the average SNR is relatively-high for
low-frequency channels/subcarriers (the lowest-frequency being
channel/subcarrier 1) and decreases as the frequency increases (the
highest-frequency being channel/subcarrier 8). In other example
implementations, noise, imperfections, and/or other characteristics
of the CATV network may result in SNR measurements which do not
necessarily decrease monotonically across channels/subcarriers.
[0038] The CMTS 102 may utilize the data corresponding to graphs
242.sub.1-242.sub.8 shown when determining physical layer
communication parameters to be used for each of the
channels/subcarriers. In an example implementation, the physical
layer parameters for a channel/subcarrier may be selected such that
all CMs in the service group can successfully receive transmissions
to the service group. Lower SNR may require, for example, lower
modulation order, lower FEC code rate, and/or higher transmit
power. In such an implementation, the graphs in FIG. 2E may result
in the following selection of physical layer parameters: for
subcarrier 1, parameters that enable reception with a tolerable
amount of errors at an SNR of 7; for subcarrier 2, parameters that
enable reception with a tolerable amount of errors at an SNR of 6;
for subcarrier 3, parameters that enable reception with a tolerable
amount of errors at an SNR of 4; for subcarrier 4, parameters that
enable reception with a tolerable amount of errors at an SNR of 6;
for subcarrier 5, parameters that enable reception with a tolerable
amount of errors at an SNR of 3; for subcarrier 6, parameters that
enable reception with a tolerable amount of errors at an SNR of 2;
for subcarrier 7, parameters that enable reception with a tolerable
amount of errors at an SNR of 3; for subcarrier 8, parameters that
enable reception with a tolerable amount of errors at an SNR of
1.
[0039] In another example implementation, for each
channel/subcarrier, the parameters may be selected such that
reception on the subcarrier requires a value of a metric (e.g., SNR
value) that a predetermined number or percentage of the CMs
reported they are unable to achieve. In this manner, other CMs may
receive higher throughput at the expense of some CMs having a
higher number of receive errors. The errors for the CMs that have
insufficient metric value for the selected parameters may be
compensated through unicast and/or multicast transmission of
replacement data and/or additional error correction bits as
discussed below. For example, assuming that it is acceptable for
five of the sixteen CMs in FIG. 2E to fall below the threshold SNR
value corresponding to the selected physical layer parameters, the
graphs in FIG. 2E may result in the following selection of physical
layer parameters: for subcarrier 1, parameters that enable
reception with a tolerable amount of errors at an SNR of 12; for
subcarrier 2, parameters that enable reception with a tolerable
amount of errors at an SNR of 11; for subcarrier 3, parameters that
enable reception with a tolerable amount of errors at an SNR of 10;
for subcarrier 4, parameters that enable reception with a tolerable
amount of errors at an SNR of 9; for subcarrier 5, parameters that
enable reception with a tolerable amount of errors at an SNR of 8;
for subcarrier 6, parameters that enable reception with a tolerable
amount of errors at an SNR of 7; for subcarrier 7, parameters that
enable reception with a tolerable amount of errors at an SNR of 6;
for subcarrier 8, parameters that enable reception with a tolerable
amount of errors at an SNR of 5.
[0040] In an example implementation, hierarchical modulation may be
used with coarse bits/most significant bits (MSBs) used for
sensitive and/or critical information (e.g., control messages such
as upstream and/or downstream MAPS, sync messages, packet headers,
I frames of an MPEG stream, and/or the like) and finer bits/least
significant bits (LSBs) used for less sensitive information (e.g.,
B frames of an MPEG stream). In an example implementation,
hierarchical modulation may be used with coarse bits or MSBs
utilized for broadcast messages and finer bits or LSBs used for
unicast and/or multicast messages to those CMs that have sufficient
metric value(s) (e.g., SNR value) to detect the finer bits. In an
example implementation, hierarchical modulation may be used where
MSBs and LSBs are transmitted on subcarriers that have higher SNR
and only MSBs may be transmitted on subcarriers which have lower
SNR. Subcarriers on which hierarchical modulation is used may be
those subcarriers for which the disparity between best-case SNR
(e.g., SNR reported by a CM that is closest to the CMTS) and
worst-cast SNR (e.g., SNR reported by CM that is furthest from the
CMTS, that is on a particularly noisy branch, that is behind a
defective cable or coupling element, etc.) is above a
threshold.
[0041] FIG. 3 illustrates example transmissions in an OFDM
cable/DOCSIS network in which different values of one or more
physical layer communication parameters can be used for different
transmissions. The transmissions shown may be coordinated using,
for example, upstream and/or downstream DOCSIS MAP messages. The
duration of the timeslot and/or which timeslot a transmission is
scheduled for may be controlled based on latency requirements of
the transmission and/or other transmissions in the network.
[0042] The transmission 301, which may be to and/or from one or
more CM(s) of a first service group, uses all subcarriers, a
timeslot of duration T1, and different physical layer parameters
("parms M" where M corresponds to the subcarrier index) for each of
the eight subcarriers. The transmission 302, which may be to and/or
from one or more CM(s) of a second service group, uses only the
three highest-frequency subcarriers, a timeslot of duration T1+T2,
and uses the same physical layer parameters ("parms 8") on each of
the three subcarriers. The transmission 303 uses the lower five
subcarriers, a timeslot of duration T1, and a different set of
physical layer parameters ("parms M" where M corresponds to the
subcarrier index) on each of the five subcarriers. The transmission
304 uses the lower five subcarriers, a timeslot of duration T2, and
a two sets of physical layer parameters ("parms 4" and "parms 2").
The transmission 305 uses only the lowest frequency subcarrier, a
timeslot of duration 2T1+2T2, and a single set of physical layer
parameters. During time interval over which transmission 305 takes
place, circuitry of the CMTS 102 and/or the CMs which may be
required for receiving on the seven higher-frequency subcarriers
may be powered down to conserve energy. The transmission 406 uses
the all of the subcarriers, a timeslot of duration T2+T1, and the
same physical layer parameters ("parms 5") on each of the
subcarriers.
[0043] In an example implementation, the physical layer parameters
may be configured to enable sleep duty cycling of CMs and/or other
components of the network. For example, the physical layer
parameters may be configured to maximize throughput while
minimizing transmission time such that more time can be spent in a
sleep/low-power mode.
[0044] FIG. 4 illustrates an example implementation in which
error-correcting bits are sent on higher-SNR subcarriers to
compensate for reception errors on lower-SNR subcarriers. In FIG.
4, the line 406 corresponds to the SNR profile of a cable modem
112.sub.X, and line 408 corresponds to the SNR required on each
subcarrier in order to successfully receive broadcast transmissions
(i.e., receive with a tolerable number of errors). For simplicity
of illustration, the required SNR is flat across the subcarriers.
In the implementation depicted, CM 112.sub.X has excess SNR in
channels/subcarriers 1-4 (the excess capacity corresponding to area
404), but has inadequate SNR in channels/subcarrier 5-8 (the
capacity deficit corresponding to area 410). Consequently, data
received on channel/subcarriers 5-8 may have unacceptably high
error rates. To compensate for the deficiency on
channels/subcarriers 5-8, replacement data and/or additional parity
bits for the packets transmitted on subcarriers 5-8 may be
transmitted on subcarriers 1-4 (e.g., in the form of a unicast
transmission, or multicast transmission where other CMs also have a
deficit on the same subcarriers). CM 112.sub.X may receive a
broadcast packet, process the broadcast packet to recover a portion
of a message, receive a unicast or multicast packet containing an
additional and/or replacement portion(s) of the message, process
the unicast and/or multicast packet to recover the additional
and/or replacement portion(s), and combine the additional and/or
replacement portions with the portion recovered from the broadcast
packet to reconstruct the message with an acceptable number of
errors.
[0045] In an example implementation, a cable modem termination
system (CMTS) (e.g., 102) may communicate with a plurality of cable
modems (e.g., 112.sub.1-112.sub.5) using a plurality of orthogonal
frequency division multiplexed (OFDM) subcarriers (e.g.,
subcarriers 1-8 of FIG. 4). The CMTS may determine a performance
metric of each of the cable modems. For each one of the plurality
of OFDM subcarriers and each one of the cable modems, the CMTS may
select physical layer parameters to be used for communication with
the one of the cable modems on the one of the OFDM subcarriers
based on a performance metric of the one of the cable modems.
Parameters may be selected for each individual cable modem (e.g., a
separate selection for each of CMs 112.sub.1-112.sub.5) or for
groups of cable modems (e.g., a first selection for CMs
112.sub.1-112.sub.3 and a second selection for CMs 112.sub.4 and
112.sub.5). The performance metric may be a signal-to-noise ratio
(SNR) profile across the OFDM subcarriers. The plurality of cable
modems may belong to a single service group, and the physical layer
parameters may be selected such that a threshold SNR required for
receiving a packet broadcast to the service group is higher than a
subset of the SNR profiles corresponding to a subset of the cable
modems. The contents of the broadcast packet may be fully or
partially retransmitted to the subset of modems in a unicast or
multicast packet.
[0046] Continuing with this example implementation, the selecting
the physical layer parameters may include selecting whether to use
hierarchical modulation for communication with the one of the cable
modems. The CMTS may select use of hierarchical modulation for a
particular one of the OFDM subcarriers when a difference between a
performance metric measured for a first one of the cable modems on
the particular one of the OFDM subcarriers and a the performance
metric measured for a second one of the cable modems on the
particular one of the OFDM subcarriers is greater than a
predetermined amount. The CMTS may communicate with the cable
modems using hierarchical modulation, wherein both of more
significant bits and less significant bits are transmitted on a
first subset of the OFDM subcarriers for which each of the modems
has a relatively-high value of a performance metric, and only more
significant bits are transmitted on a second subset of the OFDM
subcarriers for which one or more of the modems has a
relatively-low of a performance metric.
[0047] Continuing with this example implementation, the CMTS may
select the physical layer parameters such that there is excess
capacity on a first subset of the OFDM subcarriers and a capacity
deficit on a second set of the OFDM subcarriers. The CMTS may
transmit, on the first subset of the OFDM subcarriers, parity bits
for packets sent on the second subset of the OFDM subcarriers. The
CMTS may transmit, on the first subset of the OFDM subcarriers,
replacement bits for packets sent on the second subset of the OFDM
subcarriers. The physical layer parameters may include one or more
of: transmit power, receive sensitivity, timeslot duration,
modulation type, modulation order, forward error correction (FEC)
type, and FEC code rate.
[0048] Other embodiments of the invention may provide a
non-transitory computer readable medium and/or storage medium,
and/or a non-transitory machine readable medium and/or storage
medium, having stored thereon, a machine code and/or a computer
program having at least one code section executable by a machine
and/or a computer, thereby causing the machine and/or computer to
perform the steps as described herein for a high capacity CATV
network.
[0049] Accordingly, the present invention may be realized in
hardware, software, or a combination of hardware and software. The
present invention may be realized in a centralized fashion in at
least one computing system, or in a distributed fashion where
different elements are spread across several interconnected
computing systems. Any kind of computing system or other apparatus
adapted for carrying out the methods described herein is suited. A
typical combination of hardware and software may be a
general-purpose computing system with a program or other code that,
when being loaded and executed, controls the computing system such
that it carries out the methods described herein. Another typical
implementation may comprise an application specific integrated
circuit or chip.
[0050] The present invention may also be embedded in a computer
program product, which comprises all the features enabling the
implementation of the methods described herein, and which when
loaded in a computer system is able to carry out these methods.
Computer program in the present context means any expression, in
any language, code or notation, of a set of instructions intended
to cause a system having an information processing capability to
perform a particular function either directly or after either or
both of the following: a) conversion to another language, code or
notation; b) reproduction in a different material form.
[0051] While the present invention has been described with
reference to certain embodiments, it will be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted without departing from the scope of the present
invention. In addition, many modifications may be made to adapt a
particular situation or material to the teachings of the present
invention without departing from its scope. Therefore, it is
intended that the present invention not be limited to the
particular embodiment disclosed, but that the present invention
will include all embodiments falling within the scope of the
appended claims.
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